1. The Field of the Invention
The present invention relates to semiconductor devices and the manufacture thereof. More particularly, the present invention is directed to a method for forming self-aligned integrated circuit structures employing a protective layer having a horizontal top surface.
2. The Relevant Technology
Self-aligned structures in an integrated circuit may be formed by shielding previously formed structures with a protective layer of a material that resists the etchant which is used to form spaces for the self-aligned structures. The protective layer shields underlying previously formed structures from the etchant, effectively preventing the etchant from etching away around the structures to be protected. Thus the alignment of the mask to the previously formed structures is much less critical, hence the name "self-aligned". Such self-aligned structures allow denser spacing of circuit devices.
For successful formation of self-aligned structures such as self-aligned contact structures, the protective layer must adequately withstand the etchant which forms the spaces in which the self-aligned structures are to be formed. If a protective layer is etched through in the case of self-aligned contacts for example, the contact structures formed subsequently will contact inappropriate areas, resulting in shorted, non-functional circuit devices.
Protective layers over underlying structures are most vulnerable at top edges of the protective layer. Reducing the protective layer's tendency to be etched through at such top edges would thus provide an important advantage, allowing the production of dense self-aligned circuit designs with increased process control and higher yield.